The present disclosure relates to methods for determining or monitoring the amount of metal contaminants imparted into semiconductor wafers during processing and, particularly, for monitoring the amount of metal contamination imparted during wafer processing operations such as polishing, cleaning, oxide stripping and the like by subjecting a silicon-on-insulator structure to the semiconductor process, precipitating metal contamination in the structure and delineating the metal contaminants.
Metal contamination in semiconductor wafers is detrimental as the contamination can cause yield losses in the resulting integrated circuits. Metal contamination has increasingly become a concern in view of the trend toward smaller devices, devices with faster operational speeds and lower manufacturing costs. Metal contamination may be introduced into semiconductor wafers in a number of processing steps including wafer polishing, cleaning, bond strength enhancing thermal treatment, epitaxy, oxide stripping, plasma activation, wet chemical etching, gas phase chemical etching, high temperature annealing, ion implantation, oxidation and the like.
Current methods for characterizing surface metal contamination involve contacting the wafer with an extraction fluid such as water or aqueous HF. Typically a drop of fluid is contacted with the wafer surface. During the contact period metals dissolve into the extraction fluid. The fluid may be analyzed by suitable means such as inductively coupled plasma mass spectrometry (ICP-MS) in which a plasma is used to produce ions which may be detected by a mass spectrometer. This detection method is limited in that it generally cannot detect contaminants at a concentration of less than 108 atoms/cm2. Moreover, conventional surface metal detection methods are unable to provide spatial distribution information regarding contaminants on the wafer surface. Bulk metal detection methods (e.g., bulk silicon digestion plus ICP-MS and SIMS depth profile methods) also are characterized by low sensitivity.
There is a continuing need for methods for characterizing metal contamination induced during various wafer manufacturing steps including, for example, polishing, cleaning, etching and the like and for methods that detect contamination below 108 atoms/cm2 and/or that are capable of providing spatial distribution information relating to contaminants on the wafer surface.